8.5 x 20 v nose auto transfer switch

Converting Cargo Trailers into TTTs

8.5 x 20 v nose auto transfer switch

Postby Splatterman » Wed May 01, 2024 9:32 pm

Good evening fellow builders. Running a WFCO 8955 30 amp breaker box this comes with the AC to DC converter/ carger. Also installing 2 320w solar panels and a 24v battery bank. I bought the 30 amp GO Power transfer switch. So I routed the 120v power lead from the converter/ charger to the shore power positive in the transfer switch so It wasn't trying to charge the batteries with battery. My question now is how do I run the 12v to the switch? through the inverter first? But then how do I convert back to 12v at the breaker is there some way to bypass the converter/charger and just run straight to the 12v side of the panel? Sorry hope this makes any sense. There is a second post to run a 12v pos but then what happens when I'm plugged into shore would it still pull from the battery? My end goal is to not inverter 12v to 110v just to convert back to 12v and I also don't want to try and charge the battery's while not plugged into Shor power maybe I'm just over thinking it. :(
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Re: 8.5 x 20 v nose auto transfer switch

Postby Grummy » Wed May 01, 2024 11:12 pm

................. maybe I'm just over thinking it.

Hard to follow what your saying..... Lets see if I get this right.

1. You have an RV style 12 volt Power Supply/ Battery Charger (but you say you are going to have 24v battery(s) ?)

2. You have an automatic 120v transfer switch that stays on shore power until you unplug the shore power, at which time it automatically pulls from an Inverter (but obviously, only if turned on).

3. Your going to have 640 watts of solar on the roof, charging a 24v battery, and you have concerns about charging your battery with the RV Supply/ Charger because it will automatically be turned ON when the transfer switch goes over to use the Inverter.

So far, I'd assume the RV charger has a fuse in that panel and I would just PULL THE FUSE OUT and not use it. It wont really work with your 24v battery system anyhow.

Heck, if you have 620 watts of solar, I'd let Solar charge the batteries. If you don't over battery, your solar panels will be adequate. (200ah is a good target for 600 watts of panels)

Now, if that thing does not have any way to turn that power supply section of it off, just don't wire it to charge the batteries at all. Especially so if your going lithium because both the voltage is wrong as well as the charging Profile.

Now, if you want to use the 12v from the Power supply/charger for 12v lighting or accessories, I'd probably put in a simple DPDT or tumbler switch so you can choose between the power supply when your on shore power, or your DC-DC 24v to 12v drop down converter (I assume you are planning on that because what else can you do with 24v ?) In this case, the 12v NEVER even goes to the battery.

I don't know how many AH battery your planning on or what your loads are going to be. So, you still have to think about how your 640 watts is going to perform. If you are afraid that your battery may not get enough sunlight each day to fully charge because of your load/needs, you probably will have to buy a 24v Lithium charger (oh, I sure hope your going lithium because the other options really fall short these days in comparison).

I'm not sure I would like an automatic transfer that works the way yours does in a mobile application. Those are primarily designed to be used in homes where if the power drops out, an Inverter or alternate source can keep things running. I just use a 4 position tumbler switch to choose which depending on situation. I can have shore, Inverter, Genset or OFF with the twist of the wrist. When I am on Inverter, all the outlets in the trailer are on Inverter, Shore when on Shore, or Generator when on Generator. ALL my 12v lighting and Accessories are strictly on battery power all the time. IF I would ever end up with 4 of fog and the battery is not going to recover, I simply plug the ac cord of a 30A Victron Lithium charger into a source, be it shore or Generator.

Recently, I've been using a different kind of "automatic switch" on my home solar system. It's a "MOES Power controller" found on Amazon. I don't think anyone else makes this.

This unit transfers from Inverter TO Shore when your battery voltage drops below a level you can set. In other words, it can use your inverter all the time unless your battery voltage drops and then it switches over to shore. That is what I want..... I mean I paid money to build a solar system, and I want to use it as much as possible. So, If I get 4 days of no sun and the battery goes down to the point I set, it switches over to shore for me without me even bothering to know. Excellent unit because I can go away and know that my refrige and freezers will stay running. When the battery comes back up to a set point, it switches back. Now if Shore power is out, Yep, I have to be there with Generator in hand if the solar is down.

MOES has two units, a basic manual set 50a and an 80a with bluetooth. I bought the cheap one. Love it so far.

Does ANY of the above help ???
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